Question

Show transcribed image textSometimes we need a current source for which the current is independent of VBE (Because VBE varies with temperature). Derive an expression for the current Io in the circuit given below and show that it is independent of VBE. Assume all transistors are identical, that VBE is the same for all transistors, and that the base currents are negligible. Hints: Q1 and Q3 form a current mirror and recall from Electronics I, that for a BJT: IE = (beta + l) IB, Ic = beta IB and IE = IB + Ic